Process of compressing vapor in multistage centrifugal compressors



B. GRAEMIGER. Paocxsss or coMPREsslNe vAPon |N Mumsmae cENTmFuGALcommsssons.

APPLICATION FILED NOV- 3, |920. LOOl 3 Patented Dec. 20, 1921.

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BENJAMIIN GRAEMXGER, OF ZUB/10H, SWITZERLAND.

PROCESS OF COMPRESSING VAPOR IN MULTISTAGE CENTRIFUGAL COMPRESSORS.

Application filed November 3, 1920. Serial No. 421,578.

T 0 all LU tom t may concern e it known. that l, BENJAMIN GRAEMIGER, acitizen of the Re Qublicof Switzerland, residing at Zurich,Vlardturmstrasse 19, Switzerland, have invented certain new and usefulimprovements in a Process for Compressing Vapor in ll/lultistageCentrifugal Compressors; and I do hereby declare the following to be aclear, full, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame, reference being had to the accompanying drawings and to letters orfigures of reference marked thereon, which form a part of thisspecification.

This invention relates to a process for compressing vapor in multi-stagecentrifugal compressors.

According to the invention a liquid of the same nature as the vapor tobe compressed is introduced into the compressor behind at least one ofthe rotor wheels in such a form and quantity that the state of the vaporwill be changed into that in which it contains not more than three percent. by weight of liquid. The process may be carried out so that thecooling of the vapor which has been superheated through being compressedis only effected to such an extent as to obtain saturated vapor.

It is already known with air compressors of the piston type to injectwater into the air to prevent too high a rise of the temperature andtherefore of thexpower consumption. For this purpose the air from acertain stage of the compressor has been led into a special receiverinto which the water has been injected whereafter the cooled air hasbeen introduced into the next stage of the piston comf the water were tobe pumped immediately into the piston compressor the danger exists thatthe injected quantity may be too large and that water hammer occurswhich Vmight cause a bursting of the compressor. The withdrawing andre-introducing of the air from and to a special receiver causesconsiderable losses of energy. Moreover it is disadvantageous in mostcases to get moist air by this direct injection of water. In certaincases this direct injection is inadmissible especially when the air isused for combustion because a considera-ble portion of the energycontained in the fuel is then used for evaporating the particles ofSpeecaton of Letters Patent.

Patented Bec.. 260, 192i.

water contained in the air and is thus utilized inefliciently forcombustion purposes.

The conditions for carrying into eii'ect the process according to thepresent invention are quite diderent. flhe liquid injected into thecompressed vapor being of the same nature as that of which the vapor isformed, the injected liquid i. c. the cooling liquid, cannot have anyharmful ei'lect but it increases the useful quantity of vapor obtained.The mixing of liquid and vapor takes place in the rotary compressoritself without the vapor being withdrawn from the compressor in acomplicated way and then reintroduced into the latter. @nly vcare has tobe taken that the ratio between the injected liquid andf the compressedvapor is chosen such that the vaporous mixture does not contain morethan three per cent. by weight of liquid. lt is a well known fact thatwith compressing vapors in rotary compressors the vapor leaving anyrotor wheel or diffuser connected to the latter is superheated,therefore such a quantity of liquid may be injected that the vapor iscooled down from its initial highly superheated state to approximatelyits saturated state. If too great a quantity of liquid were injectedparticles of water might be admixed in a considerable quantity. to thevapor worked upon by the lfollowing rotor wheel which water4 wouldcorrode the blades of the rotor wheel and acceleration would have to beimparted to the water by the folhereinafter when explainingtheconstructional examples for carryingout the process.

With a given circumferential speed and a given number of stages, forinstance with a six-stage centrifugal compressor, an increase inpressure vof approximately 6%may be obtained by injecting liquid. Onaccount of the comparatively low initial temperatures in front ofk thevarious 4rotor wheels the theoretical and also the actual powerV usedfor compressing a given Weight of vapor, measured at the discharge end,is smaller than it Vno cooling liquid wereinjected. `When coolino'compressed air by injecting` water waste energy in the shape of heat Viscarried away by the' heated up water; in the present process, however,the

energy supplied to the vapor in certrit'ugal compressors is not lost butis utilized in generating vapor of the same kind. This increase -ofvaporniay amount to LES-5% of the weight of vapor entering the suctionend of the compressor. As the highest temperature occurring` isconsiderably lower than if no liquid were injected, the mean temperatureof the compressor casing is lower and consequently its radiation of heatand theV energy losses resulting therefrom Vare smaller.

Y All the advantages inherent to the present process are of specialimportance in the compression of'lye vapors for the purpose of utilizingsuch vapors as heat generating means whenV evaporating fresh lye.

The above mentioned advantages are all the more apparent the higher theratio of compression 1s. Y A

The liquid to be injected consists prefer ably of very pure'condensedvapor formed at any point along the path of the vapor.

The increase of the temperature of said i from 600 to 1200 kilogramsperhour, the

ordinates representV the corresponding pressure ratio of the finalpressure p2 to the initialv pressure p1. The curves I, II and IIIrepresent lthe relationfbetween the pressure ratio and the weight ofsteam with a givenY compressor running lat aV uniform speed, The curvesI and II show the presf sure-ratios obtained in a compressorl inrelation to the weights of steam entering the suction end of thecompressor, curve I in particular indicates the conditions prevailingVwith, compressions without .the Vuse of l cooling water and curve IIshowsl the conditions for compressions with cooling water injected,v Itis to be seen fromthe diagram that with the same quantity of steamenter- `ingthe suction end otthe compressorfor instance 1000' kilogramsper hour the ratio (g'be'tween the final and the vinitial pres- 1 j ,Y YY sure is 1.6 if no cooling water is introduced ,duringthe' compressionand Y1.7 6 if cooling water is introduced; The distance between thecurves II and I illustrates the gain in the ratio betweenthe pressuresby the introduction of a Vcooling liquid. The curve III indicated indotted lines gives a Vmeasure for the gain in the quantities of vaporobtained by the injection of cooling water. The distance A-k-B shows thegain in the pressure ratio with a constant quantity of steam of 1000kgs/hour at the suction end of the compressor, the horizontal distanceB-CIO kilograms per hour indicates the increase of the weight of steamin the compressor while maintaining the pressure ratio which correspondsto the ordinate of the point B. The point C shows the higher pressureratio attained in the same compresser running at the saines speedl fandthe greater weight of vapor leaving the compressor as compared with theworking of the compressor without the introduction of cooling liquid e.point A).

Fig. 2 illustrates in a vertical longitudinal section the upper part ofa four-stage centrifugal compressor, through the Vbranch 1 of which thesteam toi'be compressed enters, whichjiscompressed consecutively calpart 33; further the extended party 34 of the rod causes the water fedthrough branch 35 to the nozzle casing to leave the latter in the shapeof a hollow jet. In this manner the water offers a large surface onwhich the steamcan act so that the water is finely atomized in a veryshort time and is,

at least for the greatest part, evaporated. Y

Fig. 4- illustrates the lower half of a 'four stage centrifugalvcompressor, in which a modification of` the supply' of the cooling waterinto the path of the steam is shown, whereby the conduits 7 and SjofFig.` 2 can be dispensed with. A small auxiliary pump 11 forces waterthrough the `pipe112 into a collecting space 13 into Vwhich the highlycompressed steam enters on leaving the last rotorwheel 5. Thewater'accumulates at the bottom of thecollectingspace 13.- Part of: saidwater is evaporated'by being in contact with the highly compressed steamand con# tributes Yto lower the temperature of said steam. IAS, however,only a small portion of the steam contacts with thecomparatively smallsurfaceo'f the-water and as ittalres a certain-'time in order toevapora-te a given VVquantity of water a Small straraggqlfe` of lwatercan be easily maintained at 14 by supplying continuously fresh waterthrough pipe 12, although the steam contained in the space 13 is eitherslightly superheated, saturated or containing a quantity of liquidamounting to not more than 3 per cent. by weight. In the lowest part ofthe casing by-pass channels 16, 17, 18 are arranged by the interposition of a covering plate 15, through which channels water from thestorage 14 flows to the space 19 on account of the difference inpressure between spaces 13 and 19. At the bottom of space 19 the watercollects and forms a storage 20. In a similar manner water is flowingfrom space 19 to space 21 and from there to space 23 through a channel22 which may for instance be arranged horizontally. From the space 23the water enters finally the suction space 25 through the channel 24.Out of space 25 the water is drawn through the suction pipe 26 by thepump 11 and thereupon repeats its circuit.

If the quantity of water delivered by the pump 11 is too great, part ofit can be returned to the suction pipe 26 through pipe 27. rllhequantity of cooling water evaporated in the compresser is replaced byfresh water, which enters the suction pipe 26 by means of the pipe 28.In order to prevent the water on entering the space 19 through channel18 from squirting too high and from getting admiXed to the steam in theshape of drops of water whereby the runner wheel 5 would have to dealnot only with steam but also with water, a baffle plate 29 in the shapeof an angle iron may for example be secured to the casing above thechannel 18. Too great an evaporation and splashing of the water can alsobe prevented by providing a sieve above the stored water. Thismodification isshown bv way of example in the space 23 of Fig. 4 in avertical longitudinalV section and in Fig. 5 in a vertical crosssectionalong line D-E of Fig. 4. The sieve 30 is fixed to the compresser casingat such an elevation that it is only a small distance above the normalwater level. A sufficient exchange of heat from the steam compressed inthe rotor wheel 2 to the stored water can take place through theopenings of the sieve; the steam generated from said water rises throughthe openings of the sieve into the large space 23 where it mixes withthe compressed steam, thereby preventing an eX cessive increase of thetemperature of the latter'. Furthermore the sieve prevents that thesteam rotating in the space 23 in the direction of arrow IV carries awayparticles of water and causes a wave in the water as indicated by arrowV shown in dotted lines, whereby the water would be admixed to the steamin the shape of drops.

I claim:

1. A process for compressing vapor in multistage centrifugalcompressors, comprising introducing into the compressor behind at leastone of the runner wheels such a quantity of a liquid of the same natureas the vapor as to obtain a compressed vapor that does not contain morethan three per cent. by weight of liquid.

2. A process for compressing vapor in multi-stage centrifugalcompressors, comprising introducing into the compressor behind at leastone of the runner wheels such a quantity of liquid of the same nature asthe vapor to cool the vapor superheated in one runner wheel to itssaturated state and to obtain a compressed vapor that contains Y notmore than three per cent. by weight of liquid.

3. A process for compressing vapor in multi-stage centrifugalcompressors, comprising introducing into the compressor behind at leastone of the runner wheels such a quantity of liquid of the same nature asthe vapor in a finely distributed state to obtain a compressed vaporthat contains not more than three per cent. by weight of liquid.

4. A process for compressing vapor in multi-stage centrifugalcompressors, comprising introducing into the compressor behind at leastone of the runner wheels such a quantity of liquid of the same nature asthe vapor in the shape of hollow jets to obtain a compressed vapor thatcontains not more than three per cent. by weight of liquid.

In testimony that I claim the foregoing as my invention, I have signed mname.

BENJAMIN GRAEMIGER.

